Staphylococcus epidermidis ΔSortase A strain elicits protective immunity against Staphylococcus aureus infection.

Staphylococcus aureus and Staphylococcus epidermidis are two of the most significant opportunistic human pathogens, causing medical implant and nosocomial infections worldwide. These bacteria contain surface proteins that play crucial roles in multiple biological processes. It has become apparent that they have evolved a number of unique mechanisms by which they can immobilise proteins on their surface. Notably, a conserved cell membrane-anchored enzyme, sortase A (SrtA), can catalyse the covalent attachment of precursor bacterial cell wall-attached proteins to peptidoglycan. Considering its indispensable role in anchoring substrates to the cell wall and its effects on virulence, SrtA has attracted great attention. In this study, a 549-bp gene was cloned from a pathogenic S. epidermidis strain, YC-1, which shared high identity with srtA from other Staphylococcus spp. A mutant strain, YC-1ΔsrtA, was then constructed by allelic exchange mutagenesis. The direct survival rate assay suggested that YC-1ΔsrtA had a lower survival capacity in healthy mice blood compare with the wild-type strain, indicating that the deletion of srtA affects the virulence and infectious capacity of S. epidermidis YC-1. YC-1ΔsrtA was then administered via intraperitoneal injection and it provided a relative percent survival value of 72.7 % in mice against S. aureus TC-1 challenge. These findings demonstrate the possbility that YC-1ΔsrtA might be used as a live attenuated vaccine to produce cross-protection against S. aureus.

Sortase-catalyzed transformations that improve the properties of cytokines.

Recombinant protein therapeutics often suffer from short circulating half-life and poor stability, necessitating multiple injections and resulting in limited shelf-life. Conjugation to polyethylene glycol chains (PEG) extends the circulatory half-life of many proteins, but the methods for attachment often lack specificity, resulting in loss of biological activity. Using four-helix bundle cytokines as an example, we present a general platform that uses sortase-mediated transpeptidation to facilitate site-specific attachment of PEG to extend cytokine half-life with full retention of biological activity. Covalently joining the N and C termini of proteins to obtain circular polypeptides, again executed using sortase, increases thermal stability. We combined both PEGylation and circularization by exploiting two distinct sortase enzymes and the use of a molecular suture that allows both site-specific PEGylation and covalent closure. The method developed is general, uses a set of easily accessible reagents, and should be applicable to a wide variety of proteins, provided that their termini are not involved in receptor binding or function.

Logic-Based Delivery of Site-Specifically Modified Proteins from Environmentally Responsive Hydrogel Biomaterials.

The controlled presentation of proteins from and within materials remains of significant interest for many bioengineering applications. Though "smart" platforms offer control over protein release in response to a single external cue, no strategy has been developed to trigger delivery in response to user-specified combinations of environmental inputs, nor to independently control the release of multiple species from a homogenous material. Here, a modular semisynthetic scheme is introduced to govern the release of site-specifically modified proteins from hydrogels following Boolean logic. A sortase-mediated transpeptidation reaction is used to generate recombinant proteins C-terminally tethered to gels through environmentally sensitive degradable linkers. By varying the connectivity of multiple stimuli-labile moieties within these customizable linkers, YES/OR/AND control of protein release is exhaustively demonstrated in response to one and two-input combinations involving enzyme, reductant, and light. Tethering of multiple proteins each through a different stimuli-sensitive linker permits their independent and sequential release from a common material. It is expected that these methodologies will enable new opportunities in tissue engineering and therapeutic delivery.

Sortagged anti-EGFR immunoliposomes exhibit increased cytotoxicity on target cells.

PURPOSE: Conventional chemotherapy is associated with therapy-limiting side effects, which might be alleviated by targeted chemotherapeutics such as immunoliposomes. The targeting ligands of immunoliposomes are commonly attached by unspecific chemical conjugation, bearing risk of structural heterogeneity and therewith related biological consequences. Chemoenzymatic methods may mitigate such risks through site-specific conjugation. METHODS: The formulation parameters for pentaglycine-modified, doxorubicin-loaded liposomes and the reaction conditions for a site-specific, Sortase-A mediated conjugation with monoclonal antibodies were thoroughly evaluated. The cytotoxicity of such sortagged, epidermal growth factor receptor (EGFR)-specific immunoliposomes was tested on human breast cancer cells. RESULTS: Sortaggable liposomes with a defined size (140 nm, PDI < 0.25) and high encapsulation efficiency (>90%) were obtained after manufacturing optimization. A ratio of 1.0-2.5 µM mAb/100 µM pentaglycine yielded stable dispersions and circumvented carrier precipitation during ligand grafting. The cytotoxicity on EGFR+ MDA-MB-468 was up to threefold higher for EGFR-specific immunoliposomes than for the nontargeted controls. CONCLUSIONS: Sortase-A is suitable to generate immunoliposomes with a site-specific ligand-carrier linkage and hence improves chemical homogeneity of targeted therapeutics. However, the sweet spot for manufacturability utilizing mAbs with two Sortase-A recognition sites is narrow, making mono-reactive binders such as scFvs or Fab's preferable for a further development. Despite this, the immunoliposomes demonstrated a targeted delivery of doxorubicin, indicating the potential to increase the therapeutic window during the treatment of EGFR+ tumors.

Investigation on the reaction conditions of Staphylococcus aureus sortase A for creating surface-modified liposomes as a drug-delivery system tool.

BACKGROUND/AIM: This study aimed to determine the preferred conditions for the transpeptidase reaction of sortase A from Staphylococcus aureus, for the purpose of creating functional liposomes useful for a drug-delivery system (DDS). MATERIALS AND METHODS: His-tagged recombinant sortase A with 59 amino acids deleted from the N-terminus (His-ΔN59SrtA) was prepared using an Escherichia coli expression system. The pH dependency and sorting signal sequence dependency of the transpeptidase reaction of His-ΔN59SrtA were analyzed by monitoring the transfer of model donor-substrates (i.e. His-tagged mutant green fluorescent proteins with a C-terminal LPxTG sorting signal) to model acceptor-beads with a GGGGGC peptide. In addition, using preferred conditions, the sortase A reaction was used to modify liposome surface. RESULTS AND DISCUSSION: The transpeptidase reaction of His-ΔN59SrtA was enhanced under weakly acidic conditions. Transfer efficiency, based on sorting signal recognition by His-ΔN59SrtA, was similar to or higher than that obtained using several substrates with amino acids other than Glu in the sorting signal position "x". Furthermore, liposomes containing GGGGGC peptide-linked dipalmitoylphosphatidylethanolamine were successfully modified using the preferred conditions for His-ΔN59SrtA determined in this study. CONCLUSION: Preferred conditions for the transpeptidase reaction of His-ΔN59SrtA, especially in a weakly acidic environment to enhance reaction, was established and successfully used to create functional liposomes applicable to DDS.

Sortase A induces Th17-mediated and antibody-independent immunity to heterologous serotypes of group A streptococci.

Group A streptococci (GAS) are associated with a variety of mucosal and invasive human infections. Recurrent infections by highly heterologous serotypes indicate that cross-serotype immunity is critical for prevention of GAS infections; however, mechanisms underlying serotype-independent protection are poorly understood. Here we report that intranasal vaccination of mice with Sortase A (SrtA), a conserved cell wall bound protein, reduced colonization of nasal-associated lymphoid tissue (NALT) by heterologous serotypes of GAS. Vaccination significantly increased CD4+ IL-17A+ cells in NALT and depletion of IL-17A by neutralizing antibody prevented GAS clearance from NALT which was dependent on immunization with SrtA. Vaccination also induced high levels of SrtA-specific antibodies; however, immunized, B cell-deficient mice cleared streptococcal challenges as efficiently as wild type mice, indicating that the cross-serotype protection is Th17-biased and antibody-independent. Furthermore, efficient GAS clearance from NALT was associated with a rapid neutrophil influx into NALT of immunized mice. These results suggest that serotype independent immune protection against GAS mucosal infection can be achieved by intranasal vaccination with SrtA and enhanced neutrophil function is critical for anti-GAS defense and might be a target for prevention of GAS infections.

Protection against pneumococcal infection elicited by immunization with glutamyl tRNA synthetase, polyamine transport protein D and sortase A.

Protein-based vaccines are considered to be the next-generation of pneumococcal vaccines. Here we evaluated the protection elicited by immunization with recombinant glutamyl tRNA synthetase (Gts), polyamine transport protein D (PotD) and sortase A (SrtA) antigens in preclinical mouse models. In mucosal immunization studies, intranasal immunization with either Gts, PotD or SrtA could significantly reduce pneumococcal nasopharyngeal and lung colonization and significantly increase mice survival times following invasive pneumococcal challenge, and combinations of these antigens could enhance this protection. In systemic immunization studies, intraperitoneal immunization with multiple protein antigens also provided better protection against pneumococcal sepsis caused by different pneumococcal strains. Finally, passive immunization studies showed an additive effect by using multiple anti-sera when compared to single anti-sera. Therefore, a multicomponent protein-based pneumococcal vaccine composed of Gts, PotD or SrtA could confer protection against pneumococcal colonization as well as invasive infections in terms of efficacy of protection and serotype coverage.